Power converter between halogen transformer and LED

ABSTRACT

Control circuits ( 1 ) bring power converters ( 4 ) in different modes in response to detection results. The power converters ( 4 ) exchange possibly rectified first voltage/current signals with electronic halogen transformers ( 2 ) and supply second voltage/current signals to light emitting diode circuits ( 5 ). The first current signals have, in different modes, different amplitudes. The different amplitudes have different constant values and/or different derivative values. As a result, the first current signal has become a relatively varying first current signal. Then, the halogen transformers ( 2 ) no longer experience problems that occur when smaller amounts of power need to be provided than designed to. The detections may comprise polarity detections of and/or zero-crossing detections in the first voltage signals. The halogen transformers ( 2 ) comprise self-oscillating switched mode power supplies designed to provide first amounts of power at their outputs. The light emitting diode circuits  5 ) are designed to consume second amounts of power smaller than the first amounts.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§371 of International Application No. PCT/IB13/059885, filed on Nov. 4,2013, which claims the benefit of U.S. Provisional Patent ApplicationNo. 61/731,946, filed on Nov. 30, 2012. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a control circuit for controlling at least apart of a power converter. The invention further relates to a device, toa method, to a computer program product and to a medium.

Examples of such a power converter are single stage converters, dualstage converters, single boost converters, single buck converters,combinations of boost and buck converters, power regulators, currentregulators and current limiters etc. Examples of such a device are thepower converters mentioned above and lamps comprising one or more lightemitting diodes etc.

BACKGROUND OF THE INVENTION

WO 2011/033415 A1 discloses an illumination device comprising a powerinput stage, a power buffer stage, a driver and a light emitting diodecircuit. The power input stage, the power buffer stage and the drivercould be considered to form a power converter.

When replacing a halogen lamp by a light emitting diode circuit whilekeeping the halogen transformer, problems may occur with the halogentransformer, owing to the fact that the halogen transformer is designedto provide a first amount of power to the halogen lamp, which firstamount of power will usually be larger than a second amount of powerthat is consumed by the light emitting diode circuit. Halogentransformers require a minimum output power to perform well, and lightemitting diode circuits require for example three to ten times lesspower than halogen lamps to produce a similar amount of light.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a control circuit forimproving a situation wherein a power converter is exchanging firstvoltage and current signals or rectified versions thereof with anelectronic halogen transformer and wherein the power converter issupplying second voltage and current signals to a light emitting diodecircuit. Further objects of the invention are to provide a device, amethod, a computer program product and a medium.

According to a first aspect, a control circuit is provided forcontrolling at least a part of a power converter, the power convertercomprising an input for exchanging first voltage and current signals orrectified versions thereof with an electronic halogen transformer, andthe power converter comprising an output for supplying second voltageand current signals to a light emitting diode circuit, the controlcircuit comprising a detector for detecting an amplitude of at least oneof the first voltage and current signals, and the control circuitcomprising a controller for in response to a detection result from thedetector bringing the power converter into different modes, the firstcurrent signal in the different modes having different amplitudes, thedifferent amplitudes comprising different constant values and/ordifferent derivative values.

The power converter may be connected to the electronic halogentransformer via a rectifier, in which case the power converter willreceive rectified versions of the first voltage and current signals fromthe electronic halogen transformer. Alternatively, the rectifier mayform part of the power converter, in which case the power converter willreceive the first voltage and current signals from the electronichalogen transformer more directly.

The detector detects an amplitude of at least one of the first voltageand current signals. Usually, the detector will detect the amplitude ofthe first voltage signal, and the first current signal can then becontrolled. Thereto, the controller will bring the power converter inresponse to a detection result from the detector into different modes.In respective (subsequent) first and second modes, the first currentsignal has respective first and second amplitudes that are differentfrom each other. The respective first and second amplitudes may haverespective first and second constant values that are different from eachother or respective first and second derivative values that aredifferent from each other or both. As a result, a relatively non-varyingprior art first current signal has been converted into a relativelyvarying first current signal. The electronic halogen transformer, whileproviding such a varying first current signal, no longer experiences theproblems, such as its oscillation fading out or being terminated, thatusually occur when a constant value of the relatively non-varying priorart first current signal is given a too low value to reduce an amount ofpower supplied from the electronic halogen transformer to the powerconverter.

A light emitting diode circuit comprises one or more light emittingdiodes of whatever kind(s) and in whatever combination(s).

An embodiment of the control circuit is defined by the controller beingarranged to (de)activate at least a part of the power converter and/orto change a behavior of at least a part of the power converter forrealizing the different subsequent modes. The (de)activation of at leasta part of the power converter may for example comprise a (de)activationof a small part such as a transistor or an impedance or a (de)activationof a large part such as a group of transistors or a stage or a(de)activation of the entire power converter etc. The behavior of atleast a part of the power converter may for example comprise a timingbehavior or a frequency behavior or an impedance behavior or ahysteretic behavior or an inductive behavior (when comprising aninductor) or a capacitive behavior (when comprising a capacitor) or a(de)charge behavior (when (de)charging an inductor or a capacitor) etc.

An embodiment of the control circuit is defined by an average value ofthe first current signal, in case the control circuit is operating,being smaller than an average value of the first current signal, in casethe control circuit is not operating. This way, the electronic halogentransformer provides a smaller amount of power than designed to provide.

An embodiment of the control circuit is defined by a detection of theamplitude of the at least one of the first voltage and current signalscomprising a polarity detection and/or a zero-crossing detection.Usually, the detector will detect the amplitude of the first voltagesignal, such as subsequent polarities of the first voltage signal orsuch as subsequent zero-crossings of the first voltage signal. Adetection of one polarity may be considered to coincide with one half ofa cycle of the first voltage signal and may provide two subsequentzero-crossings indirectly owing to the fact that the zero-crossings willtake place just before and just after a duration of this one polarity.In case a zero-crossing needs to be detected more precisely, subsequentpolarities could be detected. One polarity change is a good indicationof a zero-crossing. The zero-crossings can then be found between apositive polarity and a negative polarity, and vice versa. Twosubsequent polarity changes of the first voltage signal and/or twosubsequent zero-crossings of the first voltage signal are goodindications of one half of a cycle of the first voltage signal.Similarly, the amplitude of the first current signal may be detected.

An embodiment of the control circuit is defined by the controller beingarranged to introduce at least two entire different modes during onehalf of a cycle of the first voltage signal. Preferably, for reasons ofstabilization, one entire mode should not coincide with a zero-crossingor a polarity-change of the first voltage signal. At least two entiremodes are necessary for creating the relatively varying first currentsignal.

An embodiment of the control circuit is defined by the controller beingarranged to define an amount of power supplied to the light emittingdiode circuit via a definition of a timing of the modes and/or via adefinition of the constant values. The timing and/or the constant valuesmay be used to adapt an average value of the first current signal. Anadaptation of the average value of the first current signal results inan adaptation of an amount of power supplied from the electronic halogentransformer to the power converter.

An embodiment of the control circuit is defined by the different modescomprising

-   -   a first mode wherein an amplitude of the first current signal        has a first constant value and a second mode wherein an        amplitude of the first current signal has a second constant        value larger than the first constant value,    -   a first mode wherein an amplitude of the first current signal        has a first constant value and a second mode wherein an        amplitude of the first current signal has a second constant        value smaller than the first constant value and a third mode        wherein an amplitude of the first current signal has a third        constant value larger than the second constant value,    -   a first mode wherein an amplitude of the first current signal        has a first constant value and a second mode wherein an        amplitude of the first current signal has a first positive        derivative value and a third mode wherein an amplitude of the        first current signal has a first negative derivative value,    -   a first mode wherein an amplitude of the first current signal        has a first negative derivative value and a second mode wherein        an amplitude of the first current signal has a first positive        derivative value and a third mode wherein an amplitude of the        first current signal has a second negative derivative value and        a fourth mode wherein an amplitude of the first current signal        has a second positive derivative value,    -   a first mode wherein an amplitude of the first current signal        has a first constant value and a second mode wherein an        amplitude of the first current signal has a second constant        value larger than the first constant value and has a first        positive derivative value, and/or    -   a first mode wherein an amplitude of the first current signal        has a constant value and a second mode wherein an amplitude of        the first current signal has a first positive derivative value        and a third mode wherein an amplitude of the first current        signal has a first negative derivative value and a fourth mode        wherein an amplitude of the first current signal has a second        positive derivative value and a fifth mode wherein an amplitude        of the first current signal has a second negative derivative        value.

For each one of the six cases, two or more of the different modes maytrade places, smaller and larger constant values may trade places,constant values may be replaced by derivative values, and vice versa,and positive derivative values may be replaced by negative derivativevalues, and vice versa. And for each two or more of the six cases, apart of one of them and a part of another one of them may be combined.

An embodiment of the control circuit is defined by the control circuitfurther comprising a further detector for detecting a value of the firstvoltage signal or a rectified version thereof and/or a value of thefirst current signal or a rectified version thereof. Instantaneousand/or average values of the first voltage and current signals orrectified versions thereof might be used for controlling amounts ofpower supplied to the light emitting diode circuit.

An embodiment of the control circuit is defined by the controller beingarranged to change an amount of power supplied to the light emittingdiode circuit via a definition of a timing of the modes and/or via adefinition of the constant values in response to a detection result fromthe further detector. Again, but now further in response to a detectionresult from the further detector, the timing and/or the constant valuesmay be used to adapt an average value of the first current signal.

An embodiment of the control circuit is defined by the control circuitfurther comprising a start-up circuit for adapting at least one of thefirst voltage and current signals. Such a start-up circuit improves aperformance of a combination of the control circuit and the powerconverter, such as a power factor and/or an efficiency in non-dimmingapplications.

An embodiment of the control circuit is defined by the electronichalogen transformer comprising a self-oscillating switched mode powersupply designed to provide a first amount of power at its output, thelight emitting diode circuit being designed to consume a second amountof power, the second amount being smaller than the first amount.

According to a second aspect, a device is provided comprising thecontrol circuit as defined above and further comprising the powerconverter and/or the light emitting diode circuit.

According to a third aspect, a method is provided for controlling atleast a part of a power converter, the power converter comprising aninput for exchanging first voltage and current signals or rectifiedversions thereof with an electronic halogen transformer, and the powerconverter comprising an output for supplying second voltage and currentsignals to a light emitting diode circuit, the method comprising a stepof detecting an amplitude of at least one of the first voltage andcurrent signals, and the method comprising a step of in response to adetection result from said detecting bringing the power converter intodifferent modes, the first current signal in the different modes havingdifferent amplitudes, the different amplitudes comprising differentconstant values and/or different derivative values.

According to a fourth aspect, a computer program product is provided forperforming the steps of the method as defined above.

According to a fifth aspect, a medium is provided for storing andcomprising the computer program product as defined above.

A basic idea is that the first current signal should be a relativelyvarying first current signal.

A problem to provide a control circuit for improving a situation whereina power converter is exchanging first voltage and current signals orrectified versions thereof with an electronic halogen transformer andwherein the power converter is supplying second voltage and currentsignals to a light emitting diode circuit has been solved.

A further advantage is that the different modes introduce additionalcontrol options.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a first embodiment of a control circuit connected to apower converter coupled to an electronic halogen transformer via arectifier and coupled to a light emitting diode circuit,

FIG. 2 shows a second embodiment of a control circuit connected to apower converter coupled to an electronic halogen transformer via arectifier and coupled to a light emitting diode circuit,

FIG. 3 shows an embodiment of an electronic halogen transformer,

FIG. 4 shows an analysis of the electronic halogen transformer,

FIG. 5 shows first waveforms,

FIG. 6 shows second waveforms,

FIG. 7 shows third waveforms,

FIG. 8 shows an embodiment of a power converter,

FIG. 9 shows fourth waveforms,

FIG. 10 shows fifth waveforms,

FIG. 11 shows sixth waveforms, and

FIG. 12 shows seventh waveforms.

DETAILED DESCRIPTION OF EMBODIMENTS

In the FIG. 1, a first embodiment of a control circuit 1 is shown. Thecontrol circuit 1 is connected to a power converter 4 for supplying amode signal to the power converter 4 for bringing the power converter 4into different modes. Optionally, the control circuit 1 may receive abuffer signal from the power converter 4. An input of the powerconverter 4 is coupled to an electronic halogen transformer 2 via arectifier 3 for exchanging rectified versions of first voltage andcurrent signals with the electronic halogen transformer 2.Alternatively, the rectifier 3 may form part of the power converter 4 inwhich case the power converter 4 and the electronic halogen transformer2 exchange the first voltage and current signals more directly. Anoutput of the power converter 4 is coupled to an input of a lightemitting diode circuit 5 for supplying second voltage and currentsignals to the light emitting diode circuit 5. The control circuit 1controls at least a part of the power converter 4.

The control circuit 1 comprises a detector 11 for detecting an amplitudeof at least one of the first voltage and current signals, and comprisesa controller 12 for in response to a detection result from the detector11 bringing the power converter 4 into the different modes. In thedifferent modes, the first current signal has different amplitudes. Thedifferent amplitudes comprise different constant values (differentlevels) and/or different derivative values (different shapes).

Preferably, the controller 12 (de)activates at least a part of the powerconverter 4 and/or changes a behavior of at least a part of the powerconverter 4 for realizing the different modes. Preferably, an averagevalue of the first current signal, in case the control circuit 1 isoperating, will be smaller than an average value of the first currentsignal, in case the control circuit 1 is not operating.

In the FIG. 1, further an embodiment of the detector 11 is shown. Here,the detector 11 comprises a transistor with a control electrode coupledvia a resistor and a diode to one of the output terminals of theelectronic halogen transformer 2. A first main electrode of thetransistor is connected to ground, and a second main electrode of thetransistor is connected to the controller 12 and is coupled via anotherresistor to a voltage supply terminal. However, many other embodimentsof the detector 11 will be clear to a person skilled in the art and arenot to be excluded.

Preferably, a detection of the amplitude of the at least one of thefirst voltage and current signals comprises a polarity detection ofand/or a zero-crossing detection in the first voltage signal.Preferably, the controller introduces at least two entire differentmodes during one half of a cycle of the first voltage signal.

The detector 11 shown in the FIG. 1 detects one polarity. Owing to thefact that the zero-crossings will take place just before and just aftera duration of this one polarity, this detector 11 indirectly alsoprovides the zero-crossings. However, in case these zero-crossings needto be detected more precisely, two detectors 11 identical to the oneshown in the FIG. 1 may be used, a first one coupled to a first terminalof the input of the rectifier 3 and a second one coupled to a secondterminal of the input of the rectifier 3. The zero-crossings can then befound between a positive polarity and a negative polarity, and viceversa.

In the FIG. 2, a second embodiment of a control circuit 1 is shown. Thissecond embodiment differs from the first embodiment in that the controlcircuit 1 further comprises a further detector 13. The further detector13 for example detects a value of a rectified version of the firstvoltage signal via a voltage determination circuit 14 that for examplecomprises a serial connection of two resistors in parallel to the inputof the power converter 4 by measuring a voltage at the interconnectionbetween the resistors, with one of the resistors possibly beingconnected in parallel to a capacitor. Alternatively, a value of the(non-rectified) first voltage signal may be detected. The furtherdetector 13 for example detects a value of a rectified version of thefirst current signal via a current determination circuit 15 that forexample comprises a resistor connected serially to a terminal of theinput of the power converter 4 by measuring a voltage across thisresistor. Alternatively, a value of the (non-rectified) first currentsignal may be detected. Further alternatively, the circuits 14 and/or 15may form part of the power converter 4.

A detection of the rectified first voltage signal could reveal anunbalance in a capacitive half bridge of the electronic halogentransformer. The unbalance of the capacitive half bridge can be activelycorrected by detecting the unbalance and adjusting the currentamplitudes per half a cycle of the first voltage signal. The detectionof the rectified first voltage signal may also reveal an envelope of atransformed mains voltage which may also contain some phase cut dimminginformation.

The system further comprises a start-up circuit 16 for adapting at leastone of the first voltage and current signals. Thereto, the start-upcircuit 16 is located between the output terminals of the electronichalogen transformer 2 and the input terminals of the rectifier 3. Here,the start-up circuit 16 is shown outside the control circuit 1 andoutside the electronic halogen transformer 2, alternatively, thestart-up circuit 16 may be located inside the control circuit 1 and/ormay be located inside the electronic halogen transformer 2. The start-upcircuit 16 can inject a start-up current pulse into the electronichalogen transformer 2, in case the electronic halogen transformer 2 hasstopped oscillating. The start-up current pulse initiates a start-up ofthe oscillation. This way, the oscillation of the electronic halogentransformer 2 can be controlled from its secondary side. The start-upcircuit 16 improves a performance of the electronic halogen transformer2, but is not necessarily present, owing to the fact that inside theelectronic halogen transformer 2 an initiating unit is present. Theinitiating unit, as shown in the FIG. 3, also initiates a start-up ofthe oscillation, but at a (much) lower initiation frequency than thestart-up circuit 16 can do. Further, the start-up circuit 16 can becontrolled advantageously, contrary to the initiating unit, that isusually not controlled.

The controller 12 receives first detection signals from the detector 11and receives second detection signals from the further detector 13 andsupplies a start-up signal to the start-up circuit 16.

In the FIG. 3, an embodiment of an electronic halogen transformer 2 isshown, in a simplified version. The electronic halogen transformer 2comprises two transistors 21 and 22. A first main electrode of thetransistor 21 is coupled to a voltage supply terminal to be coupled tothe mains possibly via a filter not shown and usually forming part ofthe electronic halogen transformer 2 and/or possibly via a dimmer. Thevoltage supply terminal is further coupled to one side of a capacitor23. A second main electrode of the transistor 21 is coupled to a firstmain electrode of the transistor 22. A second main electrode of thetransistor 22 is coupled to ground or another reference voltage. Anotherside of the capacitor 23 is coupled to one side of a capacitor 24, andanother side of the capacitor 24 is coupled to ground or the otherreference voltage. A first winding of a first transformer 25 isconnected to the control electrode and the second main electrode of thetransistor 21. A second winding of the first transformer 25 is connectedto the control electrode and the second main electrode of the transistor22. A third winding of the first transformer 25 is coupled to the secondmain electrode of the transistor 21 and to one side of a first windingof a second transformer 26. Another side of the first winding of thesecond transformer 26 is coupled to the other side of the capacitor 23.A second winding of the transformer 26 is coupled to a unit 27, thatrepresents a combination of the rectifier 3 and the power converter 4and in addition either a halogen lamp (prior art) or the light emittingdiode circuit 5. Two or more units 27 connected in parallel to eachother are not to be excluded. Finally, an initiating unit 28 known inthe art is coupled to the voltage supply terminal and to the controlelectrode of the transistor 22.

In the FIG. 4, an analysis of the electronic halogen transformer 2 isshown, in a simplified version. Compared to the FIG. 3, the secondtransformer 26 and the unit 27 have been replaced by a resistor 54, andthe first transformer 25 has been replaced by an inductor 53 coupled inparallel to a first diode 51 representing the junction from the controlelectrode to the first main electrode of the transistor 21 and coupledin parallel to a second diode 52 representing the junction from thecontrol electrode to the first main electrode of the transistor 22.

In the FIG. 5, first waveforms are shown (prior art). In view of theFIGS. 1-5, the graph A1 represents a first voltage signal at an outputof the electronic halogen transformer 2, and the graph A2 represents acurrent signal flowing through the inductor 53. The graph B1 representsa first current signal flowing from the output of the electronic halogentransformer 2 to the rectifier 3, the graph B2 (decreasing line)represents a current signal flowing through the diode 51, and the graphB3 (increasing line) represents a current signal flowing through thediode 52. Clearly, the first current signal (the graph B1) has, althoughalternating, a constant amplitude.

In the FIG. 6, second waveforms are shown. In view of the FIGS. 1-5, thegraph C1 represents a first voltage signal at an output of theelectronic halogen transformer 2, and the graph C2 represents a currentsignal flowing through the inductor 53. The graph D1 represents a firstcurrent signal flowing from the output of the electronic halogentransformer 2 to the rectifier 3, the graph D2 (decreasing lines)represents a current signal flowing through the diode 51, the graph D3(increasing lines) represents a current signal flowing through the diode52, the graphs E and F represent polarity detections and/orzero-crossing detections, and the graph G represents different modes ofthe power converter 4. Here, firstly, a first mode is introduced (thegraph D1 is equal to zero), thereafter a second mode is introduced (thegraph D1 is unequal to zero), followed by a time-interval resulting fromparasitics. Then the first and second modes and the parasitictime-interval are repeated etc. The first current signal (the graph D1)has got a pulsed shape here.

More in general, in the FIG. 6, there is a first mode wherein anamplitude of the first current signal has a first constant value and asecond mode wherein an amplitude of the first current signal has asecond constant value larger than the first constant value etc.

In the FIG. 7, third waveforms are shown. In view of the FIGS. 1-5, thegraph H1 represents a first voltage signal at an output of theelectronic halogen transformer 2, and the graph H2 represents a currentsignal flowing through the inductor 53. The graph I1 represents a firstcurrent signal flowing from the output of the electronic halogentransformer 2 to the rectifier 3, the graph I2 (decreasing lines)represents a current signal flowing through the diode 51, the graph I3(increasing lines) represents a current signal flowing through the diode52, the graphs J and K represent polarity detections and/orzero-crossing detections, and the graph L represents different modes ofthe power converter 4. Here, firstly, a first mode is introduced (thegraph I1 is unequal to zero), thereafter a second mode is introduced(the graph I1 is equal to zero), then a third mode is introduced (thegraph I1 is unequal to zero), followed by a time-interval resulting fromparasitics. Then the first and second and third modes and the parasitictime-interval are repeated etc. The first and third modes may beidentical modes or not. The first current signal (the graph I1) has gota pulsed shape here.

More in general, in the FIG. 7, there is a first mode wherein anamplitude of the first current signal has a first constant value and asecond mode wherein an amplitude of the first current signal has asecond constant value smaller than the first constant value and a thirdmode wherein an amplitude of the first current signal has a thirdconstant value larger than the second constant value etc.

In the FIG. 6, the controller 12 is arranged to at least introduce oneentire first mode and one entire second mode during one half of a cycleof the first voltage signal (one pulse per half a cycle of the firstvoltage signal). In the FIG. 7, the controller 12 is arranged to atleast introduce one entire first mode and one entire second mode and oneentire third mode during one half of a cycle of the first voltage signal(two pulses per half a cycle of the first voltage signal). Again, thethird mode may be identical to the first mode or not.

In the FIG. 8, an embodiment of a power converter 4 is shown. This powerconverter 4 comprises a boost converter 41 and a buck converter 42, aninput of the buck converter 42 being coupled to an output of the boostconverter 41. Between both converters 41 and 42, a storage capacitor 43may sometimes be present, and a voltage determination circuit 44 forexample similar to the circuit 14 for monitoring an indication of anamount of stored energy present in the storage capacitor 43 may bepresent. Alternatively, the storage capacitor 43 and/or the circuit 44may form part of the boost converter 41 or the buck converter 42. Thecontrol circuit 1 is connected to the boost converter 41 for supplyingthe mode signal to the power converter 4 and is connected to the circuit44 for receiving the buffer signal from the power converter 4 and isconnected to the buck converter 42 for supplying to and/or receiving apulse width modulation signal from the power converter 4 for furthercontrol etc. Many other embodiments of the power converter 4 are not tobe excluded, such as single stage converters, dual stage converters,single boost converters, single buck converters, power regulators,current regulators and current limiters etc.

In the FIG. 9, fourth waveforms are shown. In view of the FIGS. 1-5, thegraph M1 represents a first voltage signal at an output of theelectronic halogen transformer 2, and the graph M2 represents a currentsignal flowing through the inductor 53. The graph N represents arectified first current signal flowing from an output of the rectifier 3to an input of the power converter 4. Here, firstly, a first mode isintroduced (the graph N is equal to zero), thereafter a second mode isintroduced (the graph N is increasing), thereafter a third mode isintroduced (the graph N is decreasing), thereafter a fourth mode isintroduced (the graph N is increasing), thereafter a fifth mode isintroduced (the graph N is decreasing), thereafter a sixth mode isintroduced (the graph N is increasing), thereafter a seventh mode isintroduced (the graph N is equal to zero) etc. The first and seventhmodes may be identical modes or not, the second, fourth and sixth modesmay be identical modes or not, and the third and fifth modes may beidentical modes or not. Here, there are six modes per one half of acycle of the first voltage signal, more than six or fewer than six arenot to be excluded.

More in general, in the FIG. 9, there is a first mode wherein anamplitude of the first current signal has a first constant value and asecond mode wherein an amplitude of the first current signal has a firstpositive derivative value and a third mode wherein an amplitude of thefirst current signal has a first negative derivative value etc.

In the FIG. 10, fifth waveforms are shown. In view of the FIGS. 1-5, thegraph O1 represents a first voltage signal at an output of theelectronic halogen transformer 2, and the graph O2 represents a currentsignal flowing through the inductor 53. The graph P represents arectified first current signal flowing from an output of the rectifier 3to an input of the power converter 4. Here, firstly, a first mode isintroduced (the graph P is decreasing), thereafter a second mode isintroduced (the graph P is increasing), thereafter a third mode isintroduced (the graph P is decreasing), thereafter a fourth mode isintroduced (the graph P is increasing), thereafter a fifth mode isintroduced (the graph P is decreasing), thereafter a sixth mode isintroduced (the graph P is increasing) etc. The first and third andfifth modes may be identical modes or not, and the second and fourth andsixth modes may be identical modes or not. Here, there are six modes perone half of a cycle of the first voltage signal, more than six or fewerthan six are not to be excluded.

More in general, in the FIG. 10, there is a first mode wherein anamplitude of the first current signal has a first negative derivativevalue and a second mode wherein an amplitude of the first current signalhas a first positive derivative value and a third mode wherein anamplitude of the first current signal has a second negative derivativevalue and a fourth mode wherein an amplitude of the first current signalhas a second positive derivative value etc.

In the FIG. 11, sixth waveforms are shown. In view of the FIGS. 1-5, thegraph Q1 represents a first voltage signal at an output of theelectronic halogen transformer 2, and the graph Q2 represents a currentsignal flowing through the inductor 53. The graph R represents arectified first current signal flowing from an output of the rectifier 3to an input of the power converter 4. Here, firstly, a first mode isintroduced (the graph R is equal to zero), thereafter a second mode isintroduced (the graph R is increasing, starting from an offset). Here,there are two modes per one half of a cycle of the first voltage signal,more than two are not to be excluded.

More in general, in the FIG. 11, there is a first mode wherein anamplitude of the first current signal has a first constant value and asecond mode wherein an amplitude of the first current signal has asecond constant value (the offset) larger than the first constant valueand has a first positive derivative value etc.

In the FIG. 12, seventh waveforms are shown. In view of the FIGS. 1-5,the graph S1 represents a first voltage signal at an output of theelectronic halogen transformer 2, and the graph S2 represents a currentsignal flowing through the inductor 53. The graph T represents arectified first current signal flowing from an output of the rectifier 3to an input of the power converter 4. Here, firstly, a first mode isintroduced (the graph T is equal to zero), thereafter a second mode isintroduced (the graph T is increasing), thereafter a third mode isintroduced (the graph T is decreasing), thereafter a fourth mode isintroduced (the graph T is increasing), thereafter a fifth mode isintroduced (the graph T is decreasing), thereafter a sixth mode isintroduced (the graph T is more decreasing) etc. Here, there are sixmodes per one half of a cycle of the first voltage signal, more than sixor fewer than six are not to be excluded.

More in general, in the FIG. 12, there is a first mode wherein anamplitude of the first current signal has a constant value and a secondmode wherein an amplitude of the first current signal has a firstpositive derivative value and a third mode wherein an amplitude of thefirst current signal has a first negative derivative value and a fourthmode wherein an amplitude of the first current signal has a secondpositive derivative value and a fifth mode wherein an amplitude of thefirst current signal has a second negative derivative value etc.

The electronic halogen transformer 2 may comprise a self-oscillatingswitched mode power supply designed to provide a first amount of powerat its output, whereby the light emitting diode circuit 5 may bedesigned to consume a second amount of power, the second amount beingsmaller than the first amount. With the control circuit 1 as shown inthe FIGS. 1 and 2, this no longer is a problem.

Preferably, the controller 12 defines an amount of power supplied to thelight emitting diode circuit 5 via a definition of a timing of the modesand/or via a definition of the constant values. Further preferably, thecontroller 12 can change an amount of power supplied to the lightemitting diode circuit 5 via a definition of a timing of the modesand/or via a definition of the constant values possibly in response to adetection result from the further detector 13.

For example, in view of the FIG. 6, a first amount of power suppliedfrom the electronic halogen transformer 2 to the power converter 4 maybe increased/decreased by increasing/decreasing a duration of the secondmode, and by increasing/decreasing a constant value of the first currentsignal (D1) in the second mode.

For example, in view of the FIG. 7, a first amount of power suppliedfrom the electronic halogen transformer 2 to the power converter 4 maybe increased/decreased by increasing/decreasing a duration of the firstand third modes, and by increasing/decreasing a constant value of thefirst current signal (I1) in the first and third mode.

For example, in view of the FIG. 9, a first amount of power suppliedfrom the electronic halogen transformer 2 to the power converter 4 maybe increased/decreased by increasing/decreasing a duration of thesecond, fourth and sixth modes, and by decreasing/increasing a durationof the first, third and fifth modes.

For example, in view of the FIG. 10, a first amount of power suppliedfrom the electronic halogen transformer 2 to the power converter 4 maybe increased/decreased by increasing/decreasing a duration of thesecond, fourth and sixth modes, and by decreasing/increasing a durationof the first, third and fifth modes.

For example, in view of the FIG. 11, a first amount of power suppliedfrom the electronic halogen transformer 2 to the power converter 4 maybe increased/decreased by increasing/decreasing a duration of the secondmode, and by increasing/decreasing a constant value (here: an offset) ofthe first current signal (R) in the second mode, and bydecreasing/increasing a duration of the first mode.

For example, in view of the FIG. 12, a first amount of power suppliedfrom the electronic halogen transformer 2 to the power converter 4 maybe increased/decreased by increasing/decreasing a duration of the secondand fourth modes, and by decreasing/increasing a duration of the first,third, fifth and sixth modes.

The value of a (positive/negative) derivative value of the amplitude ofthe first current signal in a particular mode defines the slope of thefirst current signal in this mode and is usually not controlled but isdefined by one or more parameters of the electronic halogen transformer2. In view of the FIG. 12, the electronic halogen transformer 2 issolely responsible for the different negative derivative values of theamplitude of the first current signal in the fifth and sixth modes. As aresult, in view of the FIG. 12, alternatively, the fifth and sixth modesmight be considered to be identical modes and/or one and the same modeof the power converter 4. In the latter case, in the FIG. 12, there arefive modes per one half of a cycle of the first voltage signal.

So, the controller 12 may control an average value of the first currentsignal to control a first amount of power supplied from the electronichalogen transformer 2 to the power converter 4 through (de)activation ofat least a part of the power converter 4 and/or through a change in abehavior of at least a part of the power converter 4 to realize thedifferent modes. The (de)activation of at least a part of the powerconverter 4 may for example comprise a (de)activation of a small partsuch as a transistor or an impedance or a (de)activation of a large partsuch as a group of transistors or a stage or a (de)activation of theentire power converter 4 etc. The behavior of at least a part of thepower converter 4 may for example comprise a timing behavior or afrequency behavior or an impedance behavior or a hysteretic behavior oran inductive behavior (when comprising an inductor) or a capacitivebehavior (when comprising a capacitor) or a (de)charge behavior (when(de)charging an inductor or a capacitor) etc.

The waveforms in the FIG. 9 could for example be realized via a powerconverter 4 in the form of a (hysteretic controlled) boost converterwith modulated hysteretic levels, wherein an inductor charge is releasedthrough another supply path. This other supply path allows thecontroller 12 to switch off the input current of the boost converterinstantaneously. The waveforms in the FIG. 10 could for example berealized via a power converter 4 in the form of a hysteretic-controlledboost converter with a dynamic hysteresis level. This hysteresis levelis dynamically adjusted in order to track/follow a magnetizing currentof the first transformer 25. The waveforms in the FIG. 11 could forexample be realized via a power converter 4 in the form of a buck-boostconverter (also called fly-back converter). The slope between theminimum and maximum current level depends on an input voltage level andan inductor value in the electronic halogen transformer. The power leveldepends on the minimum and maximum levels and the duration of the secondmode. The waveforms in the FIG. 12 could for example be realized via apower converter 4 in the form a regular hysteretic-controlled boostconvert in combination with a pulsed load operation as also shown in theFIGS. 6 and 7 that is based on (de)activation of (a part of) the powerconverter 4 etc.

In view of the FIGS. 6, 7, 9, 11 and 12, it is observed that, in caseone half of a cycle is divided into a first part and a following secondpart, in accordance with momentary test results, preferably more averagepower will be drawn in the second part than in the first part. In viewof the FIGS. 6, 7 and 9-12, further (positive/negative) offsets may beintroduced anywhere.

Summarizing, control circuits 1 bring power converters 4 in differentmodes in response to detection results. The power converters 4 exchangepossibly rectified first voltage/current signals with electronic halogentransformers 2 and supply second voltage/current signals to lightemitting diode circuits 5. The first current signals have, in differentmodes, different amplitudes. The different amplitudes have differentconstant values and/or different derivative values. As a result, thefirst current signal has become a relatively varying first currentsignal. Then, the halogen transformers 2 no longer experience problemsthat occur when smaller amounts of power need to be provided thandesigned to. The detections may comprise polarity detections of and/orzero-crossing detections in the first voltage signals. The halogentransformers 2 comprise self-oscillating switched mode power suppliesdesigned to provide first amounts of power at their outputs. The lightemitting diode circuits 5 are designed to consume second amounts ofpower smaller than the first amounts.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed invention, from a study ofthe drawings, the disclosure, and the appended claims. In the claims,the word “comprising” does not exclude other elements or steps, and theindefinite article “a” or “an” does not exclude a plurality. The merefact that certain measures are recited in mutually different dependentclaims does not indicate that a combination of these measures cannot beused to advantage. Any reference signs in the claims should not beconstrued as limiting the scope.

The invention claimed is:
 1. A control circuit for controlling a powerconverter, the power converter connected to a light emitting diodecircuit, the control circuit comprising: a detector for detecting anamplitude of at least one of a first voltage signal and a first currentsignal which are output by an electronic transformer, and a controllerconfigured to bring the power converter into different modes, inresponse to a detection result from the detector, wherein the firstcurrent signal in the different modes comprises different amplitudes,the different amplitudes comprising at least one of: different constantvalues and different derivative values, wherein the controller isconfigured to: deactivate and activate the power converteralternatively, and change a behavior of the power converter forrealizing the different modes during each half cycle of the electronictransformer, wherein the different modes comprise: (1) a first modewherein an amplitude of the first current signal has a first constantvalue and a second mode wherein the amplitude of the first currentsignal has a second constant value larger than the first constant value,or, (2) a first mode wherein an amplitude of the first current signalhas a first constant value and a second mode wherein the amplitude ofthe first current signal has a second constant value smaller than thefirst constant value and a third mode wherein an amplitude of the firstcurrent signal has a third constant value larger than the secondconstant value, or (3) a first mode wherein an amplitude of the firstcurrent signal has a first constant value and a second mode wherein theamplitude of the first current signal has a first positive derivativevalue and a third mode wherein the amplitude of the first current signalhas a first negative derivative value, or (4) a first mode wherein anamplitude of the first current signal has a first negative derivativevalue and a second mode wherein the amplitude of the first currentsignal has a first positive derivative value and a third mode whereinthe amplitude of the first current signal has a second negativederivative value and a fourth mode wherein the amplitude of the firstcurrent signal has a second positive derivative value, or (5) a firstmode wherein an amplitude of the first current signal has a firstconstant value and a second mode wherein the amplitude of the firstcurrent signal has a second constant value larger than the firstconstant value and has a first positive derivative value, or (6) a firstmode wherein an amplitude of the first current signal has a constantvalue and a second mode wherein the amplitude of the first currentsignal has a first positive derivative value and a third mode whereinthe amplitude of the first current signal has a first negativederivative value and a fourth mode wherein the amplitude of the firstcurrent signal has a second positive derivative value and a fifth modewherein the amplitude of the first current signal has a second negativederivative value.
 2. The control circuit of claim 1, wherein theelectronic transformer comprises a first transistor and a secondtransistor, wherein the controller is configured to: deactivate thepower converter with no signal flowing from the output of the electronictransformer for a duration wherein there is a current signal flowingthrough a junction from a control electrode to a first main electrode ofthe first transistor and activate the power converter after thatduration, in each operation half cycle of the electronic transformer. 3.The control circuit of claim 1, wherein the detection result of theamplitude of the at least one of the first voltage signal and the firstcurrent signal comprises at least one of a polarity detection and azero-crossing detection.
 4. The control circuit of claim 3, wherein thecontroller is configured to introduce at least two different modesduring one half of a cycle of the first voltage signal.
 5. The controlcircuit of claim 1, wherein the controller is configured to control anamount of power supplied to the light emitting diode circuit via atleast one of a control of a timing of the modes and via a control of theconstant values.
 6. The control circuit of claim 1, the control circuitfurther comprising a further detector for detecting at least one of: avalue of the first voltage signal, a value of a rectified version of thefirst voltage signal, a value of the first current signal, and a valueof a rectified version of the first current signal.
 7. The controlcircuit of claim 6, the controller being arranged to change an amount ofpower supplied to the light emitting diode circuit via at least one of adefinition of a timing of the modes and a definition of the constantvalues, in response to a detection result from the further detector. 8.The control circuit of claim 1, the electronic transformer comprising aself-oscillating switched mode power supply configured to provide afirst amount of power at an output, and the light emitting diode circuitbeing configured to use a second amount of power, the second amountbeing smaller than the first amount.
 9. A device comprising the controlcircuit of claim 1 and further comprising the power converter, the powerconverter comprising: an input for receiving the first voltage signaland the first current which are output by the electronic transformer,and an output for supplying a second voltage signal and a second currentsignal to the light emitting diode circuit.
 10. The control circuit ofclaim 1, wherein the behavior of the power converter comprises at leastone of a timing behavior, a frequency behavior, an impedance behavior, ahysteretic behavior, an inductive behavior, a capacitive behavior, and adischarge behavior.
 11. A method for controlling a power converter, thepower converter comprising an input for receiving a first voltage signaland a first current signal or rectified versions thereof from anelectronic transformer for halogen lamps, and the power convertercomprising an output for supplying a second voltage signal and a secondcurrent signal to a light emitting diode circuit, the method comprising:detecting an amplitude of at least one of the first voltage signal andthe first current signal output by the electronic transformer; and inresponse to a detection result from said detecting, bringing the powerconverter into different modes, the first current signal in thedifferent modes having different amplitudes, the different amplitudescomprising at least one of different constant values and differentshapes, wherein the controller is arranged to deactivate and activatethe power converter alternatively during each operation half cycle ofthe electronic transformer, wherein the different modes comprise: (1) afirst mode wherein an amplitude of the first current signal has a firstconstant value and a second mode wherein the amplitude of the firstcurrent signal has a second constant value larger than the firstconstant value, or (2) a first mode wherein an amplitude of the firstcurrent signal has a first constant value and a second mode wherein theamplitude of the first current signal has a second constant valuesmaller than the first constant value and a third mode wherein theamplitude of the first current signal has a third constant value largerthan the second constant value, or (3) a first mode wherein an amplitudeof the first current signal has a first constant value and a second modewherein the amplitude of the first current signal has a first positivederivative value and a third mode wherein the amplitude of the firstcurrent signal has a first negative derivative value, or (4) a firstmode wherein an amplitude of the first current signal has a firstnegative derivative value and a second mode wherein the amplitude of thefirst current signal has a first positive derivative value and a thirdmode wherein the amplitude of the first current signal has a secondnegative derivative value and a fourth mode wherein the amplitude of thefirst current signal has a second positive derivative value, or (5) afirst mode wherein an amplitude of the first current signal has a firstconstant value and a second mode wherein the amplitude of the firstcurrent signal has a second constant value larger than the firstconstant value and has a first positive derivative value, or (6) a firstmode wherein an amplitude of the first current signal has a constantvalue and a second mode wherein the amplitude of the first currentsignal has a first positive derivative value and a third mode whereinthe amplitude of the first current signal has a first negativederivative value and a fourth mode wherein the amplitude of the firstcurrent signal has a second positive derivative value and a fifth modewherein the amplitude of the first current signal has a second negativederivative value.